1. Field of the Invention
The present invention relates to a solid-state imaging device in which a large number of photoelectric conversion elements configured to detect color components of colors, such as R (red), G (green), and B (blue), are regularly arranged on a semiconductor substrate in a row direction and in a column direction according to a predetermined array pattern.
2. Description of the Related Art
In a solid-state imaging device employed by an apparatus, such as a digital camera, a large necessary number of photoelectric conversion elements (generally, photodiodes) are arranged in a two-dimensional square lattice to detect pixels of a two-dimensional image that is an object image. Also, generally, a plurality of photoelectric conversion elements respectively corresponding to R, G, and B colors are disposed in a two-dimensional arrangement by being regularly arranged in a row direction and in a column direction according to a specific array pattern.
Actually, a plurality of photoelectric conversion elements respectively corresponding to R, G, and B colors are arranged according to an array pattern called a Bayer array so as to optimize the quality of a taken color image. Also, generally, the characteristics of colors detected by the photoelectric conversion elements are determined by color filters disposed in front of light receiving surfaces of the photoelectric conversion elements. That is, an optical filter transmitting only R-color, an optical filter transmitting only G-color, and an optical filter transmitting only B-color are disposed in front of the position of each of the photoelectric conversion elements according to the Bayer array. In the case of using the optical filters, photoelectric conversion elements having same characteristics can be employed as those corresponding to each color.
Hitherto, as disclosed in, for example, JP-A-2004-055786, a honeycomb array pattern has been formed on a silicon substrate by disposing low-sensitivity photoelectric conversion elements having a low detection sensitivity, which are arranged like a square lattice, and high-sensitivity photoelectric conversion elements having a high detection sensitivity, which are arranged like a square lattice, so that each of the low-sensitivity photoelectric conversion elements is shifted to an adjacent position to an associated one of the high-sensitivity photoelectric conversion elements.
The detection sensitivity of the photoelectric conversion element is defined as a characteristic indicating an amount of signals that can be output from a photoelectric conversion element when a predetermined amount of light is incident upon this photoelectric conversion element. That is, when the same amount of light is incident upon a high-sensitivity photoelectric conversion element and a low-sensitivity photoelectric conversion element, an amount of signals output from the high-sensitivity photoelectric conversion element, whose detection sensitivity is relatively high, is more than that of signals output from the low-sensitivity photoelectric conversion element whose detection sensitivity is relatively low. The high-sensitivity photoelectric conversion element is most suitable for taking an image of an object of low light intensity, because a relatively large amount of signals can be obtained therefrom even when a relatively small amount of light is incident thereupon. However, when a relatively large amount of light is incident thereupon, the amount of signals outputted therefrom saturates in a short period of time. Therefore, the high-sensitivity photoelectric conversion element is unsuitable for taking an image of an object of high light intensity. Conversely, the high-sensitivity photoelectric conversion element is most suitable for taking an image of an object of high light intensity, because a large amount of signals cannot be obtained therefrom even when a relatively large amount of light is incident thereupon. However, when a relatively small amount of light is incident thereupon, the amount of signals outputted therefrom is too small. Therefore, the low-sensitivity photoelectric conversion element is unsuitable for taking an image of an object of low light intensity.
A solid-state imaging device configured in this way can simultaneously utilize the low-sensitivity photoelectric conversion element and the high-sensitivity photoelectric conversion element at each of pixels to be detected. Thus, the dynamic range of the imaging device can be increased by detecting light of a relatively large amount with the low-sensitivity photoelectric conversion element and also detecting light of a relatively small amount with the high-sensitivity photoelectric conversion element.
Meanwhile, in a case where each of the low-sensitivity photoelectric conversion elements is disposed to adjoin an associated one of the high-sensitivity photoelectric conversion elements, and where the general Bayer array is employed, the photoelectric conversion elements are arranged according to the array pattern of shown in, for example, FIG. 4. In FIG. 4, characters “R”, “G”, and “B” designate a photoelectric conversion element used to detect the R-color, a photoelectric conversion element used to detect the G-color, and a photoelectric conversion element used to detect the B-color, respectively. Also, in FIG. 4, circles represent high-sensitivity photoelectric conversion elements. Squares represent low-sensitivity photoelectric conversion elements.
In the solid-state imaging device having the array pattern of the photoelectric conversion elements (for example, photodiodes, and hereunder sometimes abbreviated as “PD”) shown in FIG. 4, a PD line on which high-sensitivity photoelectric conversion elements are arranged is paired with an adjacent PD line on which low-sensitivity photoelectric conversion elements are arranged. For example, a PD line L11 of high-sensitivity photoelectric conversion elements and an adjacent PD line L21 of low-sensitivity photoelectric conversion elements constitute a paired line set PL1. Similarly, a PD line L12 of high-sensitivity photoelectric conversion elements and an adjacent PD line L22 of low-sensitivity photoelectric conversion elements constitute a paired line set PL2. A PD line L13 of high-sensitivity photoelectric conversion elements and an adjacent PD line L23 of low-sensitivity photoelectric conversion elements constitute a paired line set PL3. A PD line L14 of high-sensitivity photoelectric conversion elements and an adjacent PD line L24 of low-sensitivity photoelectric conversion elements constitute a paired line set PL4.
Accordingly, wide dynamic range image signals can be obtained by processing signals read from the photoelectric conversion elements in units of the paired line sets (PL1, PL2, PL3, . . . ) and using signals detected at a relatively low sensitivity and signals detected at a relatively high sensitivity corresponding to each color.
Meanwhile, paying attention to the color components, in the array pattern shown in FIG. 4, photoelectric conversion elements respectively detecting R-color, G-color, R-color, G-color, R-color, are arranged in this order on each of odd-numbered PD lines (L11 and L13) from the top line of a group of the PD lines of high-sensitivity photoelectric conversion elements and odd-numbered PD lines (L21 and L23) from the top line of a group of the PD lines of low-sensitivity photoelectric conversion elements. Also, photoelectric conversion elements respectively detecting G-color, B-color, G-color, B-color, G-color, . . . are arranged in this order on each of even-numbered PD lines (L12 and L14) from the top line of a group of the PD lines of high-sensitivity photoelectric conversion elements and even-numbered PD lines (L22 and L24) from the top line of a group of the PD lines of low-sensitivity photoelectric conversion elements.
That is, no photoelectric conversion elements adapted to detect B-color are provided on the odd-numbered PD lines. Also, no photoelectric conversion elements adapted to detect R-color are provided on the even-numbered PD lines. Therefore, all the color components “R”, “G”, and “B” cannot be obtained only by processing signals in units of the paired line sets. Consequently, a color image of an object cannot be reproduced. In the case of reading signals from all the photoelectric conversion elements, a lacking color component can be obtained by interpolation through image processing utilizing signals outputted from adjacent paired line sets. However, in the case of using a digital camera, due to the limitation of memory capacity and to reduction of an imaging time, it is necessary to take images of an object at the highest resolution and at a lower resolution.
In the case of taking an image of an object at a relatively low resolution, generally, when signals are read from the photoelectric conversion elements of the solid-state imaging device, thinning is performed in units of the paired line sets. For example, the reading of signals from the photoelectric conversion elements of the even-numbered paired line sets (PL2, PL4, . . . ) is omitted. That is, signals are read only from the photoelectric conversion elements of the odd-numbered paired line sets (PL1, PL3, . . . ), among the photoelectric conversion elements arranged according to the array pattern shown in FIG. 4. Thus, an image, whose longitudinal resolution is reduced by half, can be obtained.
However, photoelectric conversion elements detecting B-color are not provided on the odd-numbered paired line sets. Thus, in the case of omitting the reading of signals from the even-numbered paired line sets, on each of which photoelectric conversion elements detecting B-color are provided, a color image of an object cannot be reproduced.
Also, in the case of reading signals only from the even-numbered paired-line sets and omitting the reading of signals from the odd-numbered paired-line sets, because photoelectric conversion elements detecting R-color are not provided on the even-numbered paired-line sets, a color image of an object cannot be reproduced.
To solve the above problems, it is necessary to set paired line sets, on which the thinning is performed, so that all of the photoelectric conversion element detecting R-color, the photoelectric conversion element detecting G-color, and the photoelectric conversion element detecting B-color are included by the paired line sets from which signals are read. To perform thinning on the solid-state imaging device described in JP-A-2004-055786 so that a color image of an object can be reproduced, it is necessary to perform, for example, a process of reading signals from the paired line sets PL1 and PL2 and thinning the paired line sets PL3 and PL4. Thus, control timing is complicated. The control timing is simplest in the case of performing thinning on every other paired line set. However, no the related-art solid-state imaging devices are configured to enable such a control operation.